from sys import stdin, stdout
input = lambda: stdin.readline().rstrip()
println = stdout.write

def main():
    N = int(input())
    V = list(map(int, input().split()))

    val = [0, 0] + V
    dp = [0] * (N + 2)
    for i in range(2, N + 2):
        dp[i] = max(dp[i-1], dp[i-2] + val[i])
    print(dp[-1])

main()